Antineutrino production in a nuclear reactor can result from the fission of uranium (U) and plutonium (Pu) atoms, whereby antineutrinos result from the beta-decay of neutron-rich fragments of the respective atoms. On average, each fission reaction can produce approximately six antineutrinos. Hence, as a result, a typical nuclear power reactor can produce approximately 1022 antineutrinos per second. Monitoring of the antineutrino production rate can provide a direct measurement of the number of atoms undergoing fission, and accordingly, the thermal power and operational status of a reactor.
Detection of reactor-induced antineutrinos is usually performed through the inverse beta-decay process. In this charged current interaction, an antineutrino (ν) interacts with a quasi-free proton (p) in a hydrogenous material. The interaction results in final-state products of a positron (e+) and a neutron (n), e.g., ν+p→e++n, whereby the presence and/or existence of the positron and the neutron can be detected. The presence of a positron and an associated neutron (e.g., the positron and neutron co-exist as a function of the interaction of the antineutrino and the proton) can act as a signature of the prior existence of an antineutrino. The cross-section for this process is small (˜10−42 cm−2). However, a combination of the large flux of antineutrinos from a nuclear reactor and a moderately sized detector (a cubic meter scale detector contains ˜1028 target protons) can result in several thousand interactions per day at a standoff of 10-50 meters, which is sufficient to provide a monitoring capability.
A concern when attempting to detect antineutrinos is the large background signals generated by cosmogenic radiation (e.g. neutrons, muons, pions, gamma rays, etc.) which are produced in the earth's atmosphere. Accordingly, an approach to overcome such background radiation is to locate the monitoring system underground, and hence, reduce the number of signals being generated by background electromagnetic particles and accordingly, increase the sensitivity to signals being generated by the antineutrinos which exist as a function of the nuclear fission reactions. However, operation of such subterranean monitoring systems can be costly, operationally inflexible, and difficult to maintain.